GAS TURBINE FIRE AND EXPLOSION SAFETY ROGER SANTON

GAS TURBINE FIRE AND EXPLOSION SAFETY ROGER SANTON RETIRED HM PRINCIPAL SPECIALIST INSPECTOR OF HEALTH AND SAFETY

Size Range • 7 0 RDERS OF MAGNITUDE • 500+Mw • 1 -10 w circa one ton fuel / sec circa 0. 2 g/sec

Size Range • POWER GENERATION • 1 -1000 m. W

POWER GENERATION (SIMPLE OR COMBINED CYCLE) • HAZARDS • INCIDENTS • PRECAUTIONS

HAZARDS • • • FIRE EXPLOSION MECHANICAL NOISE ELECTRICAL & ELECTROMAGNETIC TRAPPING See ISO 21789 (ref 1)for guidance on all hazards

FIRE • FUEL FROM LEAK • GT FUEL – NATURAL GAS, OIL, LPG, NAPHTHA, BIOGAS, H 2 etc. • LUBE OIL • HYDRAULIC OIL • IGNITION • Hot surface • Mechanical spark • etc.

EXPLOSION • FUEL FROM LEAK • GAS, VAPOUR, LIQUID MIST, as a FLAMMABLE CLOUD • IGNITION • ENCLOSURE (Can be a normal ventilated enclosure or turbine hall)

GAS TURBINE INCIDENTS, UK OFFSHORE AND ONSHORE (ref. 2) YEAR FIRES EXPLOSIONS ELECTRICAL CONTROLS OTHER TOTAL FATAL INJURY GAS LEAKS 1991 4 1 1 1 7 1992 6 4 1 5 16 1993 7 12 1 20 1 1994 14 5 1 2 22 1995 14 3 2 1 2 21 1996 10 7 3 3 3 24 1 1997 7 8 2 2 5 25 1998 8 8 4 22 1999 11 4 2 1 7 24 2000 12 10 3 26 2001 7 9 1 1 2 3 21 3 2 2002 9 3 1 2 17 1 2003 4 1 1 3 9 TOTAL 113 75 13 1 12 40 254 3 5

Incident severity • Minor – very small releases, insignificant consequences, protection adequate • Significant – Potential for injury or major loss, contained or mitigated successfully • Major – Fatality, significant injury, or substantial loss

UK OFFSHORE

UK INCIDENTS

KLEEN ENERGY • FEB 7 TH 2010 • EXPLOSION AT KLEEN ENERGY SYSTEMS POWER STATION, CONNECTICUT, UNDER COMMISSIONING. • “BLOW-DOWN” OF MAIN GAS SUPPLY PIPE • 6 FATALITIES, 50 INJURED • 17 COMPANIES FINED A TOTAL OF $16. 6 M BY OSHA OVER 371 SAFETY VIOLATIONS

MITIGATION DESIGN CONSTRUCTION INSTALLATION COMMISSIONING OPERATION MAINTENANCE INSTRUCTIONS TRAINING SUPERVISION

ACTIVITY

LEAK RISK REDUCTION MINIMUM NUMBER OF JOINTS (ZERO? ) DESIGN FOR MOVEMENT, BUT MINIMISE FLEXIBLES DESIGN FOR EASE OF ASSEMBLY, INSPECTION & MAINTENANCE QA ASSEMBLY AND RE-ASSEMBLY PRESSURE TEST, LEAK TEST (ref. 3) ENCAPSULATE JOINTS FLANGE GUARDS (For liquid releases in particular) DOUBLE WALLED PIPE

LEAK DETECTION GAS DETECTION CATALYTIC IR ABSORPTION ACOUSTIC IR – VERY SENSITIVE (ref 4) LIQUID MIST DETECTION (Semi-quantitative) (Test methods - ref. 5)

SOURCES OF IGNITION HOT SURFACE AUTOIGNITION ELECTRICAL GEARBOXES, BEARINGS & FANS FLASHBACK FIRES IN FUEL PIPES PIPEWHIP BLADE AND CONTAINMENT LOSS STATIC ETC. , ETC………………….

IGNITION RISK REDUCTION AREA CLASSIFICATION SURFACE TEMPERATURE LIMITATION BY COOLING INSULATION SHIELDING

FIRE DETECTION & SUPPRESSION MINIMUM - RATE COMPENSATED THERMAL DETECTION UV, IR, SMOKE DETECTION AS APPROPRIATE CO 2 OR WATER MIST SUPPRESSION ACCESS CONTROL VENTILATION CONTROL SUPPRESSION PERSISTENCE TRIP (maintain rotation and thus lube even if on fire)

MITIGATION OF FIRE & EXPLOSION BY ENCLOSURE DESIGN LEAK RISK REDUCTION LEAK DETECTION IGNITION RISK REDUCTION FIRE DETECTION/SUPPRESSION

MITIGATION - FIRE & EXPLOSION LEAK RISK REDUCTION LIMITED LEAK TESTING LEAK DETECTION CLOUD SIZE UNKNOWN IGNITION RISK REDUCTION FIRE DETECTION/SUPPRESSION RELIABILITY ISSUES BASIS OF SAFETY AGAINST EXPLOSIONS ? ?

FINITE FORESEEABILITY OF LEAKS AND SOURCES OF IGNITION LEADING TO EXPLOSIONS BASIS OF SAFETY AGAINST EXPLOSIONS – DILUTION VENTILATION (EXPLOSION SUPPRESSION) (EXPLOSION RELIEF)

DILUTION VENTILATION • . . SHOULD QUICKLY AND EFFECTIVELEY DILUTE ANY FORESEEABLE RELEASE TO BELOW THE LEL; THERE SHOULD BE NO STAGNANT REGIONS, OR RECIRCULATION LEADING TO RE-ENTRAINMENT, AND ACCUMULATIONS OF EXPLOSIBLE MIXTURE SHOULD BE MINIMISED TO SAFE LEVELS.

DILUTION VENTILATION • Small enclosures (<50 m 3) – Smoke – Anemometer • Large enclosures – ? ? ?

DILUTION VENTILATION • Small enclosures <50 m 3) – Smoke – Anemometer • Large enclosures – CFD (ref 10)

CFD required a criterion to discriminate good from bad ventilation. HSE proposal (1996 ref. 6) was that the size of the flammable cloud from the largest undetectable gas leak, as defined by the iso-surface at 50% of LEL should be no larger than 0. 1% of the net enclosure volume.

Dilution Ventilation Criterion • ISO 21789 – First detailed appearance of dilution ventilation criterion in a standard – 5. 17. 5 - recommended CFD if surface temperatures exceed AIT of flammable gas, vapour or mist, or where risk assessment indicates a residual risk of ignition – 5. 16. 5. 3. 3 – criteria from JIP (ref. 7)

JIP Dilution Ventilation Criterion • • Based on CFD and explosion trials Gas detector in outlet duct, gas leak at trip setting 100% LEL iso-surface of cloud volume Converted to equivalent stoichiometric volume Should be less than 0. 1% of net volume of enclosure Safety factor to be based on risk assessment Hole size 0. 25 mm 2 to 25 mm 2 Based on 10 mbar enclosure strength

Dilution Ventilation Criterion • If enclosure strength can be shown to be 15 mbar cloud volume may be 0. 15% • CFD ventilation prediction to be verified • Several leak points to be modelled, using CFD to predict poorly ventilated zones

Counter- intuitive • Increased ventilation rate may be regarded as improvement • It has the effect of diluting the gas concentration at the outlet and thus leads to a larger leak to be modelled • Lower ventilation rate, if possible, reduces leak size to be modelled • Distribution of ventilation and avoidance of stagnant zones and re-entrainment are more important

ATEX

ATEX, DIRECTIVE 94/9/EC ARTICLE 1 "EQUIPMENT MEANS MACHINES. . . INTENDED FOR THE GENERATION. . . AND CONVERSION OF ENERGY. . . WHICH ARE CAPABLE OF CAUSING AN EXPLOSION THROUGH THEIR OWN POTENTIAL SOURCES OF IGNITION. " GAS TURBINES ARE INCLUDED IN THIS SCOPE

ATEX, DIRECTIVE 94/9/EC ANNEX II, PARAGRAPH 1. 3. 1 "POTENTIAL IGNITION SOURCES SUCH AS. . . HIGH SURFACE TEMPERATURES. . . AND OTHER IGNITION SOURCES MUST NOT OCCUR. “ IN EFFECT, GAS TURBINES CANNOT OPERATE IN THE ZONED AREAS CREATED BY THEIR OWN FUEL SUPPLIES Eu. MIGT REPRESENTATIONS TO EC

ATEX 2014/34/EU Guidelines extracts from para 244 • Gas turbine fuel supplies may give rise to a potentially explosive atmosphere in the vicinity of the turbine. Additionally, other sources of a potentially explosive atmosphere may also exist, e. g. lubricating oils. Equipment in category 3 of equipment-group II would usually be required in such areas. • In normal circumstances, a gas turbine could have hot surfaces above the auto ignition temperature of the fluids used. Operation under fault conditions may increase surface temperatures.

ATEX 2014/34/EU Guidelines extracts from para 244 • A gas turbine which has surface temperatures that can lead to the ignition of a potentially explosive atmosphere cannot comply with the relevant provisions of Directive 2014/34/EU. In such circumstances additional measures are required. • A number of alternatives are available for selection as a basis for safety, e. g. limitation of the volume of the explosive atmosphere by dilution ventilation , explosion relief, explosion suppression or a combination of these techniques.

AREA CLASSIFICATION • INSIDE DILUTION VENTILATED ENCLOSURE, AREA CLASSIFICATION WAS NOT REQUIRED, (BS 5345, 1983; RECOMMENDED BY IP CODE 15, 1990, PM 84) BUT ATEX II REQUIRES AREA CLASSIFICATION AND PROTECTED ELECTRICAL EQUIPMENT. • Equipment in category 3 (zone 2) of equipment-group II would usually be required. (ATEX 2014/34/EU Guidelines para 244) • For natural gas see IGEM SR 25 (ref 11)

LIQUIDS • LIQUID FUELS, LUBRICATING AND HYDRAULIC OILS • ATEX and DSEAR SPECIFICALLY APPLY TO MIST EXPLOSION POTENTIAL • RISK REDUCTION, RISK ASSESSMENT • MIST DETECTION • FLANGE GUARDS

LIQUIDS • ATEX and DSEAR SPECIFICALY APPLY TO MIST EXPLOSION POTENTIAL • AREA CLASSIFICATION REQUIRED • KEROSINE AS PROXY FOR ZONE EXTENT IN EI 15 (ref. 9) • CFD

LIQUIDS • No ATEX certified equipment or test method for mists • Use surface temperature and IP (Ingress protection)

REFERENCES 1. ISO 21789: 2009, Gas turbine applications – Safety 2. Santon, R. C. , Gas Turbine Incidents; “A Review of UK Onshore and Offshore Installations”, Trans. Institution od Diesel and Gas Turbine Engineers Gas Turbine Conference, 3 -4 October 2005. 3. Operational safety and post-maintenance gas leak detection in GE frame 9001 FA gas turbines, D A Farthing, L Marley and J A Lees, Proc. IMech. E vol. 213, Part A, 465 -474, The Institution of Mechanical Engineers. 4. Acoustic infrared, see http: //media. msanet. com/gasdetection/photoacoustic%20 chemga rd%20 white%20 pap. pdf 5. A test method for assessing the performance of oil mist detectors HSL research report RR 1059

6. Guidance Note PM 84, (revised 2003) Control of safety risks at gas turbines used for power generation, Health and Safety Executive 7. Ivings, M. J. , Lea, C. J. , Ledin, H. S. , Pritchard, D. K. , Santon, R. C. and Saunders, C. J. , “Outstanding safety questions concerning the use of gas turbines for power generation – Summary report”, 2004, HSL report CM/04/02, Health and Safety Laboratory, Buxton, UK. 8. ATEX 2014/34/EU Guidelines, section 244 9. EI Model code of safe practice Part 15: Area classification for installations handling flammable fluids, edition 4, 2015

10. Improving gas turbine power plant safety: the application of computational fluid dynamics to gas leaks, S Gilham, I R Cowan and E S Kaufman, Proc. IMech. E vol. 213, Part A, 475 - 489, The Institution of Mechanical Engineers 11. IGEM/SR/25 Hazardous area classification of natural gas installations, The Institution of Gas Engineers